Aquarium enthusiasts have searched for the perfect water treatment system that will model a natural ecosystem. Water movement, oxygen and pH control, nutrient control and waste removal are essential for a healthy, captive water ecosystem. The system must support algae, aerobic bacteria, plankton and coral growth to satisfy these requirements.
Water movement facilitates the exchange of metabolites and mimics ocean tides which rise and fall over algae covered rocks. Algae, which is required for a healthy captive ecosystem, requires water movement. Several approaches have been used to mimic natural water movement. Lee Chin Eng circulated unfiltered sea water with air bubbles in his "nature's system" to model the wave action of nature ecosystems. Wave generators have been used to create water movement but unfortunately these devices can cause splashing which upsets the salt concentration of the water. Several references disclose systems which rely partially on equilibrium or gravity for water movement. Most contemplate the use of a water pump which is disadvantageous due to plankton mortality. Plankton is required to support coral and filter feeding organisms. (See U.S. Pat. No. 5,419,831 to Fuerst et al.; U.S. Pat. No. 4,867,874 to Aubert et al.; U.S. Pat. No. 4,606,821 to D'Imperio; U.S. Pat. No. 5,096,576 to Szabo and U.S. Pat. No. 4,761,227 to Willinger et al.). Some references use an air pump to induce water flow and introduce oxygen. (See U.S. Pat. No. 5,234,581 to Rosenberg and U.S. Pat. No. 5,269,914 to Englert). Unfortunately, many of these devices also cause splashing.
Various methods and devices have been developed for controlling oxygen concentration, pH, nutrient availability and waste control. The most natural approaches have used biological filters or algae turf scrubbers. Biological filtration systems provide attachment surfaces for microorgansisms to increase biological and chemical activities.
Trickle filters are available for biological filtration. In such devices, water is typically removed from the aquarium and allowed to trickle over a bed of lava rock or plastic balls. Trickle filters provide an oxygen rich environment for the growth of aerobic bacteria because the bed is not submerged. However, trickle filters can take up a relatively large area and usually require dedicated plumbing and pump fixtures. As a result, such filters can be expensive and impractical in most applications and are not particularly useful for the average home aquarium.
Rotating biological filters are often used to support bacterial growth in home aquariums. These filter systems are partially submerged so that each portion of the media is alternately submerged and exposed to air. See U.S. Pat. No. 5,419,831 to Fuerst which discloses that the filter is rotated with a stream of water. One disadvantage of this device is that it requires a water pump. Bacterial filters are further limited because while they remove ammonia and particulate waste, they deplete oxygen and increase the concentration of nitrates and carbon dioxide.
Algae turf scrubbers address some of the limitations of biological filters in that they control oxygen concentration, pH and nutrient availability. Dr. Adey's system includes a shallow trough in fluid communication with an aquarium tank. A mesh screen in the trough supports algae growth and a wave surge bucket provides water movement. Because algae is most efficient when young, the algae must be harvested or scraped from the screen periodically. Harvesting simulates the grazing that occurs in natural systems. One disadvantage of this system, however, is that harvesting must be done manually which is labor intensive. Also, the centrifugal pumps required for these systems kill plankton and the splashing disrupts the salt concentration of the water. Furthermore, these systems require significant modifications to existing aquariums.
A need has remained for devices which connect easily to existing aquariums and support natural-type ecosystems by controlling pH, oxygen, carbon dioxide concentration, nutrient availability and waste removal without the disadvantages of splashing, killing plankton and extensive maintenance.